The quality of being narrow, or not wide.
Narrowness can make things feel tight or restricted.
Examples:
The narrowness of the path made it hard to walk.
The narrowness of the room made it feel cramped.
She didn't like the narrowness of the hallway.
The narrowness of the bed made it uncomfortable.
The narrowness of the tunnel was scary.
The narrowness of the tree branch made it hard to climb.